1. Field of the Invention
The present invention relates to a DAC (Digital to Analog Converter) for converting a digital signal into an analog signal, and more particularly, relates to a DAC for generating a transfer function having a desired notch while reducing quantization noise.
2. Description of the Background Art
In a conventional DAC, particularly, for example, in an RF DAC (Radio Frequency Digital to Analog Converter) used to be applied to a radio transmitter, quantization noise is removed by using a noise shaping technology with a delta sigma modulator, and a transfer function having a notch for reducing a signal level in a desired frequency band is generated.
For example, in Non-Patent Literature 1 (“Mismatch Shaping for a Current-Mode Multibit Delta-Sigma DAC”, T. Shui et al, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 34, NO. 3, MARCH 1999), a transfer function having a notch for reducing a signal level in a desired frequency band is generated by using a mismatch shaping technology.
However, Non-Patent Literature 1 discloses an algorithm for controlling a unit-element array on the basis of input information (amplitude information, scalar) that is information two items before in a temporal axis, as shown in FIG. 24.
In the algorithm of the conventional mismatch shaping, when a phase error occurs, a transfer function having a notch for reducing an error signal level in a desired frequency band cannot be obtained, and thus noise characteristics deteriorate.